Work is being continued along the lines of the major concern of our laboratory, the study of the contents and modes of maintenance of pools of non-protein amino acids and related substances in normal and neoplastic tissues. In addition, wherever possible, applications from our findings are being attempted in the therapy of malignant tumors in animals. The uptake of amino acids by several normal tissues and tumor cells has been studied in great detail in mice after the administration of large amounts of single amino acids. Attempts now are being made to employ substances which bind to some of the extensively accumulated amino acids intracellularly in an attempt to exert affects on the metabolic machinery of the tumor cells. Studies are being continued on the surface properties of the growing and regressing ascites tumor cells making extensive use of the microelectrophoresis techniques. During the course of these studies, protein components of the sera of the animals also are being studied by a newly devised two-dimensional gel electrophoresis technique. The influence of the host-produced antibodies and of chemical agents on the surface properties of ascites tumor cells is being examined. Chemicals are being sought that may have preferential affinity for tumor cell membranes. Application is being made of a new versatile method for measuring transaminase activities to the study of the metabolism of growing and regressing tumors. Some anti-tumor activity has been found in a naturally occurring substance, Juglone, and detailed studies are being made of the mechanism of action of this material. It appears to affect specifically some basic properties of cell membranes. Studies of epidermal carcinogenesis are continuing. Also, our finding that methyl N-carbamyl maleamate blocks the entry of RNA from nucleus to cytoplasm has led to attempts to analyze and exploit this finding.